Method and apparatus for determining exact shrink and stretch limits in rubber pad forming of curved flanged members

ABSTRACT

A form block for use in rubber pad forming has a spiral groove cut therein which forms a spiral land between adjacent convolutions of the groove having generally parallel inner and outer spiral flange forming edges. A spiral sheet metal blank which matches the spiral of the form block but is wider than the spiral land on the block is secured to the block with its spiral edges extending beyond the inner and outer edges of the land on said block to produce spiral shrink and stretch flanges on said blank during a press forming operation. By observing where on the inner and outer flanges the flanges formed become unacceptable, and measuring the radius to each of these points, the exact minimum radii contour for both shrink and stretch flanges can be determined for the material and temper condition of the sheet metal comprising the blank. A modification of the grooved form block is shown to accommodate a spiral draw ring by which draw ring data can be obtained with the same blanks.

United States Patent 1 [111 3,747,389 Harvey July 24, 1973 METHOD AND APPARATUS FOR Primary Examiner-Charles W. Lanham DETERMINING EXACT SHRINK AND STRETCH LIMITS IN RUBBER PAD FORMING OF CURVED FLANGED MEMBERS Inventor: John W. Harvey, Milford, Conn.

Assignee: United Aircraft Corporation, East Hartford, Conn.

Filed: Aug. 31, 1971 Appl. No.: 176,461

References Cited UNITED STATES PATENTS 2/1913 Vogt t t 72/476 4/1912 Stevens... 29/6l0 12/1959 Onofri 29/610 Assistant ExaminerRobert M. Rogers Attorney-Maurice B. Tasker et al.

A form block for use in rubber pad forming has a spiral groove cut therein which forms a spiral land between adjacent convolutions of the groove having generally parallel inner and outer spiral flange forming edges. A spiral sheet metal blank which matches the spiral of the form block but is wider than the spiral land on the block is secured to the block with its spiral edges extending beyond the inner and outer edges of the land on said block to produce spiral shrink and stretch flanges on said blank during a press forming operation. By observing where on the inner and outer flanges the flanges formed become unacceptable, and measuring the radius to each of these points, the exact minimum radii contour for both shrink and stretch flanges can be determined for the material and temper condition of the sheet metal comprising the blank. A modification of the grooved form block is shown to accommodate a spiral draw ring by which draw ring data can be obtained with the same blanks.

ABSTRACT 6 Claims, 12 Drawing Figures Pmmwwwm 3.147. 389 SHEET 6 (1F 7 METHOD AND APPARATUS FOR DETERMINING EXACT SHRINK AND STRETCH LIMITS IN RUBBER PAD FORMING OF CURVED FLANGED MEMBERS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method and apparatus for determining the exact shrink and the exact stretch limits of various sheet materials which are to be formed into curved members having flanges. Many such sheet metal members are used in the manufacture of aircraft and these may be of different alloys, different thickness, different temper and the flanges may vary in depth.

It has been the practice to make a large number of individual test form blocks, each with a specified contour radius. With these blocks bend radii are established for a given material, temper and thickness. Trials are then run to determine maximum flange height for the material under test. Most of this work is done by rubber pad forming and the use of dams introduces another set of variables. Several hundred test blocks with the attendant labor costs to fabricate them and catalog and evaluate the results are required to get substantial data for engineering design limits.

2. Description of the Prior Art Various attempts have been made to improve on this time consuming and costly procedure. U.S. Reissue Pat. No. Re. 1 1,421 to Erichsen, dated Jan. 8, I918, discloses one method proposed to determine the drawing quality of sheet metal. This is commonly referred to as the cup method" in which a sheet of metal is held between annular supports and a blunt die is driven against the sheet to press it into a cup shape until failure occurs.

US. Pat. No. 2,986,926, issued June 6, 1961 to E. G. Freemon shows another approach in which two mating dies are moved together with a sheet metal blank between them to produce a series of indentations in the blank of increasing depth. By examining the indentations it is possible to get some idea of how much deformation the test blank will withstand before stretch fracture, but little more. This method does not indicate anything as regards shrink limits only stretch values, and this only over a step-by-step range. Further these values are not in terms of radius of curvature of a curved member.

US. Pat. No. 3,050,991, issued Aug. 28, 1962 to E. S. Madrzyk et al. shows the bulge method of'determining the drawing quality of sheet steels. A circular diaphragm of sheet metal supported at its edges is subjected to hydraulic pressure on one side. The specimen is "bulged" until bulge height increases without further increase in hydraulic pressure. This gives a drawability index which is where failure begins.

None of these patents provide means for testing various sheet metals for exact limits in flange height and minimum contour radii for shrink and stretch flanges over a continuous range.

SUMMARY OF THE INVENTION It is a primary object of this invention to provide a method and means to physically determine simultaneously the drawing and compression qualities of a selected sheet metal over an extensive continuous range and further to determine at exactly what point in the range the limits are exceeded.

A further object of this invention is to provide a method and means to test any sheet metal of any composition any temper condition and thickness to determine exact limits in flange height and minimum contour radii for shrink and stretch flanges in rubber pad forming.

Still another object of this invention is the provision of a form block, or die, for use in rubber pad forming apparatus which has a spiral groove. into which a correspondingly slotted spiral sheet metal blank has its parallel spiral edges projected by a rubber forming block to provide shrink and stretch flanges over a wide range of gradually changing contour radii.

A further object of this invention is to provide appa ratus for testing sheet metal of various compositions, hardness and thickness to determine the limits for curved shrink and stretch flanges of different heights at different contour radii.

It is also an object of this invention to provide a form block for continuous curved shrink and stretch flange formation in rubber pad forming having a flat upper face in which a spiral groove is formed, leaving the upper surface which remains in the form of a flat spiral landhaving parallel inner and outer spiral flange forming edges.

Another object of this invention is to provide a spiral draw ring member which is receivable in the spiral groove of such a form block for use in rubber press forming to generate draw ring data on this same spiral form block.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a drill template;

FIG. 2 is a plan view ofa form block for use in rubber pad forming;

FIG. 3 is a perspective view of a router and a router template used in forming the form block of FIG. 2;

FIG. 4 is a partial cross section taken on line 4-4 of FIG. 2 showing the rubber forming block with a test blank between the form block and the forming block just prior to forming;

FIG. 5 is a similar view of the form block and the test blank following forming;

FIG. 5A is a plan view of the test blank shown in place on the form block;

FIG. 6 is a perspective view on an enlarged scale of the test blank following forming showing the shrink and stretch flanges on the blank;

FIG. 7 is a checking template used to facilitate direct reading of the minimum contour radii for shrink and stretch flanges;

FIGS. 8 and 9 are partial sectional views taken before and after forming of a modified construction for obtaining draw ring data;

FIG. 10 is a plan view of the form block ofthis modified structure; and

FIG 11 is a perspective view on an enlarged scale of the finished blank formed by this modified construction.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1, 2 and 5, numeral 10 indicates generally a thick form block, shown in cross section in FIG. 5, that may conveniently measure 48 X 48 in plan,

which is half of a standard sheet of sheet metal. The upper surface of the block 10 is flat and has formed in it a spiral groove 12 of several convolutions (FIG. 2) which extend from one of its ends 14 located adjacent the perimeter of the block to its other end 16 adjacent the center of the block. The groove is of substantial depth, as will be evident from FIG. 5. The outer end 14 of the groove is spaced from the perimeter of block 10 a sufficient distance to provide a flat land 17 surrounding the outer convolution of the groove which merges into a spiral land 17a between convolutions of the groove. In these lands holes 18 are drilled to receive tooling pins 18a shown in FIG. 3. These holes are conveniently located by means of a drill template 20 shown in FIG. 1.

Pins 18a are used to coordinate a routing template 22 with form block 10. This template has a narrow slot 24 which matches the spiral groove 12 in die 10 except for its width which is just sufficient to form a guide for a router bit. Slot 24 guides a router head 26 which is mounted so that it can swing over the entire area of form block 10. The router and router template are used to cut the relatively wide groove 12 in form block 10. They are also used to cut a narrower slot 28 (FIG. 4) in a test blank 30 (FIG. a) which with the template may be secured to block by pins 18a for this operation. The spiral slot 28 conforms to the spiral groove 12 cut in block 10 since it is cut with the same template. If desired, this operation may be performed separate from the form block. Since slot 28 is narrower than groove 12, the land 32 between its convolutions are wider than lands 17a of form block 10. Hence the test blank overhangs the spiral flange forming edges of land 17a in the form block. The outer spiral edge 34 of land 17a (FIG. 4) forms the shrink flange 36 ontest blank 30 (FIG. 5) while the inner spiral edge 38 of land 17a forms the stretch flange 40 on test blank 30.

The formed test piece shown in FIG. 6 can be removed from the die for examination of the two spiral 'flanges formed to determine the minimum contour radii for acceptable shrink and stretch flanges for the particular material and condition of hardness of the metal comprising the blank.

In practicing the invention, the form block, or die, 10

is fastened to the base plate of a rubber pad forming press (not shown) and drill template (FIG. 1) is used to locate and drill holes 18 in block 10. These holes receive pins 18a which are first used to secure router template 22 in position on the form block. Router 26 is used to cut the spiral groove in the form block. The spiral design is such that the space between the outside of a given spiral segment and the adjacent inside of the next spiral segment is just enough to allow for the maximum flange depth on each side plus the diameter of the shank of the router bit used to rout the groove. This provides the desirable "dam effect of rubber forming which will be evident from FIG. 4. Template 22 used to determine the mold line of the form block is also used as a template for forming the slot 28 in the test blank 30 by bushing the router to the desired flange height. When the spiral groove 12 has been cut in the form block and template 22 has been removed, a sheet of material to be tested, which has been drilled by tem plate 20, is placed beneath router template 22. The router is then used to cut spiral slot 28 in the test blank which registers with the spiral groove in form block 10 because the router bit is guided in cutting groove l2 and slot 28 by the same spiral slot 24 in template 22. The router template is next removed and the test sheet is secured to the form block by pins 18a. The rubber forming block is now moved against form die 10 to form the flanges on the test blank shown in FIG. 5.

Following the forming operation the test piece is removed from the form block and inspected to determine the points on the inside and outside parallel flanges 36 and 40 at which an acceptable flange becomes unacceptable. Measuring the radii to these points provides the exact minimum contour radial limits for both shrink and stretch flanges for the material of the blank tested. The former expensive and laborious series of tests, by which one can never be sure of reaching exactly the limits, is eliminated.

The form block and router template may be made of any metal or plastic material substantial enough to take the wear and forming pressures imposed by the operation. Also the form block can be made in segments fastened to a common base if a larger tool is required.

In FIG. 7 a checking template 44 is shown which is made of transparent material such as Mylar, and can be used to instantly determine the radius at any point on the test blank spiral. This template is made with a darkened spiral band 46 which exactly overlies the land 32a (FIGS. 5 and 6) of the formed test blank. This band is marked at appropriate intervals with indications 48 of the radius of curvature on the inner groove wall so that a quick determination of the radius at any given point on the test blank spiral is possible.

The method of this invention as described up to this point can be used by anyone having tools commonly found in any well-equipped shop. However, if more sophisticated equipment is available the work can be greatly facilitated by the use of a numerically (tape) controlled vertical spindle milling machine to cut out both the template 22 and the form block 10. This same machine can be used to drill the router template, the drill template and the form block. It will be evident then that neither the template 22 nor the drill template need be used in machining the form block when using the programmed tape. Also the test blank is slotted, as previously described, with the use of the template 22, an operation which can be performed remote from the forming press.

Ifthe computer data which designed the spiral for the form block is available, it can be modified and programmed into a tape for numerically controlled machining both template 22 and form'block 10 on numerically controlled equipment.

FIGS. 8, 9 and 10 illustrate a modification of the spirally grooved form block by which the form block can be used to generate draw ring data for use in evaluating the formability ofa given sheet material into shrink and stretch flanges. As shown in FIG. 10, form block 10 has pins 44 threaded into thebottom of the spiral groove 12 therein at spaced points along the groove. These pins, which extend a short distance above the top 17 of the form block, serve to locate a spiral draw ring 46 which has holes 48 so located as to register with pins 44 and guide member 46 into the spiral groove 12. The clearance between member 46 and each side of the groove in form block 10 is equal to the thickness of the sheet metal blank to be formed or in some cases slightly greater. Member 46 can be molded or machined from any suitable material which has the strength required to resist the wear and forming pressures imposed by the forming operation.

In using the draw ring 46 the blank is placed on form block with member 46 resting on the blank and with guide pins 44 projecting through the spiral slot in the blank and into holes 48 in member 46. The rubber forming block 42 as it descends moves the draw ring member 46 forcibly against the blank and, as it enters the groove 12, forms the spiral shrink and stretch flanges 36a and 40a on the blank.

The resultant test piece is shown in FIG. 11 and is evaluated in the same way that was described in connection with FIG. 6 above. It will be noted from FIG. 11 that there is no noticeable difference in the stretch flange formed by the draw ring over that illustrated in FIG. 6. However, the shrink flange of FIG. 11 shows dimpling of the metal lower down on the flange and there are flow lines higher up on the flange. The exact appearance of the shrink flange will vary with variations in the spacing between the draw ring and the sides of the spiral groove. However, a very good indication is given of the formability of the particular metal being tested, and as in FIG. 6 the exact minimum contour radii for acceptable curved flanges is clearly shown.

I wish it to be understood that I do not desire to be limited to the exact details of construction shown and described, for obvious modifications will occur to a person skilled in the art.

I claim:

1. The method of using a form block having a spiral groove in one of its surfaces to form a flanged article of spiral configuration having inner and outer spiral stretch and shrink flanges, comprising the steps of cutting a matching spiral slot in a sheet-metal blank which slot is narrower than the groove in the form block, fixing the slotted blank on said block so that the inner and outer spiral edges of said blank overlie the groove in said block, and forcing a yieldable forming member against said blank to force the over-lying edges thereof 2. Apparatus for use in resilient pad forming of curved flanged sheet-metal blanks of varying thickness temper and composition, comprising a form block with a spiral groove in one surface forming parallel inner and outer spiral flange-forming edges of gradually increasing radius over a wide range, and means for securing a sheet metal blank having a matching spiral slot which is narrower than the groove in said form block to said surface of said form block with its inner and outer spiral edges overlying said groove in said form block.

3. A form block for simultaneously forming both stretch and shrink flanges on a sheet metal test blank, said form block including a flat upper surface having a spiral groove formed therein, and a plurality of vertical guide pins in the bottom of said groove at spaced points along said groove.

4. The form block of claim 3 in which the pins extend above the flat upper surface of said block and a spiral draw ring is receivable in said groove and has vertical holes which register with the pins in said form block.

5. Apparatus for obtaining draw ring data by rubber press forming comprising a form die with a flat upper surface having a spiral groove formed therein, a plurality of guide pins secured in the bottom of said groove at spaced points along said groove, and a spiral draw ring receivable in said groove having vertical holes to receive said pins.

6. Apparatus for obtaining draw ring data by rubber press forming of curved flanged members comprising a form die with a flat upper surface on which a sheet metal blank is adapted to be supported, said die having a spiral groove formed in its flat surface in the bottom of which a plurality of vertical pins are secured at spaced points along said groove, and a spiral draw ring conforming to the spiral groove and receivable therein having vertical holes to receive said pins, said guide ring having a width which provides a clearance beinto the groove in said form block to form continuous tween it and each side wall of said groove equal at least to the thickness of the sheet metal test blank. 

1. The method of using a form block having a spiral groove in one of its surfaces to form a flanged article of spiral configuration having inner and outer spiral stretch and shrink flanges, comprising the steps of cutting a matching spiral slot in a sheet-metal blank which slot is narrower than the groove in the form block, fixing the slotted blank on said block so that the inner and outer spiral edges of said blank overlie the groove in said block, and forcing a yieldable forming member against said blank to force the over-lying edges thereof into the groove in said form block to form continuous curved shrink and stretch flanges over a wide range of continuously varying radius.
 2. Apparatus for use in resilient pad forming of curved flanged sheet-metal blanks of varying thickness temper and composition, comprising a form block with a spiral groove in one surface forming parallel inner and outer spiral flange-forming edges of gradually increasing radius over a wide range, and means for securing a sheet metal blank having a matching spiral slot which is narrower than the groove in said form block to said surface of said form block with its inner and outer spiral edges overlying said groove in said form block.
 3. A form block for simultaneously forming both stretch and shrink flanges on a sheet metal test blank, said form block including a flat upper surface having a spiral groove formed therein, and a plurality of vertical guide pins in the bottom of said groove at spaced points along said groove.
 4. The form block of claim 3 in which the pins extend above the flat upper surface of said block and a spiral draw ring is receivable in said groove and has vertical holes which register with the pins in said form block.
 5. Apparatus for obtaining draw ring data by rubber press forming comprising a form die with a flat upper surface having a spiral groove formed therein, a plurality of guide pins secured in the bottom of said groove at spaced points along said groove, and a spiral draw ring receivable in said groove having vertical holes to receive said pins.
 6. Apparatus for obtaining draw ring data by rubber press forming of curved flanged members comprising a form die with a flat upper surface on which a sheet metal blank is adapted to be supported, said die having a spiral groove formed in its flat surface in the bottom of which a plurality of vertical pins are secured at spaced points along said groove, and a spiral draw ring conforming to the spiral groove and receivable therein having vertical holes to receive said pins, said guide ring having a width which provides a clearance between it and each side wall of said groove equal at least to the thickness of the sheet metal test blank. 